Solar cell

ABSTRACT

The present disclosure provide a solar cell, including: a substrate, an interface passivation layer covering a rear surface of the substrate, and an electrode disposed at a side of the interface passivation layer facing away from the substrate, the interface passivation layer including a first interface passivation sub-layer corresponding to a portion of the interface passivation layer between adjacent electrodes and a second interface passivation sub-layer corresponding to a portion of the interface passivation layer where disposed between the substrate and the electrode; a field passivation layer, at least partially disposed between the interface passivation layer and the electrode; and a conductive enhancement layer, at least partially disposed at a side of the first interface passivation sub-layer away from the substrate to enable carriers in the first interface passivation sub-layer to flow to the electrode, where a resistivity of the conductive enhancement layer is smaller than a resistivity of the field passivation layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 17/112,850, filed on Dec. 4, 2020, which claims the benefit ofpriority to Chinese Patent Application No. 202011308762.X filed on Nov.19, 2020, each of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a photovoltaictechnique, in particular to a solar cell.

BACKGROUND

With the continuous development of the solar cell technology, arecombination loss of a metal contact area has become one of importantfactors restricting further improvement of conversion efficiency of asolar cell. In order to improve the conversion rate of the solar cell,the solar cell is usually passivated by a passivated contact in order toreduce the recombination therein and on the surface of the solar cell.Existing passivated contact cells include a heterojunction withintrinsic thin-layer (HIT) cell and a tunnel oxide passivated contact(TOPCon) cell.

However, the conversion efficiency of the existing passivated contactcells still needs to be improved.

SUMMARY

Some embodiments of the present disclosure provide a solar cell withimproved conversion efficiency.

An aspect of the present disclosure provides a solar cell, including: asubstrate; an interface passivation layer on a rear surface of thesubstrate, wherein the interface passivation layer comprises a firstinterface passivation sub-layer and a second interface passivationsub-layer; at least one electrode disposed at a side of the interfacepassivation layer facing away from the substrate, the first interfacepassivation sub-layer corresponding to a portion of the interfacepassivation layer between adjacent electrodes and the second interfacepassivation sub-layer corresponding to a portion of the interfacepassivation layer between the substrate and the at least one electrode;a field passivation layer, at least partially disposed between theinterface passivation layer and the at least one electrode; and aconductive enhancement layer, at least partially disposed at a side ofthe first interface passivation sub-layer facing away from thesubstrate, and configured to enable carriers in the first interfacepassivation sub-layer to flow to the at least one electrode, wherein aresistivity of a material of the conductive enhancement layer is smallerthan a resistivity of a material of the field passivation layer, and theresistivity of the material of the conductive enhancement layer issmaller than 0.001 Ω·cm.

In some embodiments, the conductive enhancement layer is configured tocover at least part of a surface of the first interface passivationsub-layer facing away from the substrate, and the field passivationlayer is configured to cover a surface of the conductive enhancementlayer facing away from the substrate.

In some embodiments, the field passivation layer is configured to covera surface of the second interface passivation sub-layer facing away fromthe substrate; at least part of the conductive enhancement layer isdisposed between adjacent electrodes, and the conductive enhancementlayer is in contact with a side wall of the at least one electrode. Inthis way, the carriers may flow to the electrode completely through theconductive enhancement layer without passing through the fieldpassivation layer, which is beneficial to reduce a series resistance ona transmission path of the carriers, shorten the transmission path ofthe carriers, enable the carriers to flow to the electrode at arelatively fast transmission rate and a relatively low transmissionloss, and ensure that the solar cell has a relatively high conversionefficiency.

In some embodiments, the field passivation layer is configured to covera surface of the interface passivation layer facing away from thesubstrate, wherein the field passivation layer disposed between adjacentelectrodes is a first field passivation sub-layer, and the conductiveenhancement layer is configured to cover at least part of the surface ofthe first field passivation sub-layer facing away from the substrate.Since an arrangement of the conductive enhancement layer does not changea vertical distance between the field passivation layer and thesubstrate, the field passivation layer still has a relatively good fieldpassivation effect under a condition that a concentration of a doped ionin the field passivation layer remains unchanged, thus ensuring aselective transmission of the carriers and further ensuring that thesolar cell has the relatively high conversion efficiency.

In some embodiments, the at least one electrode is configured topenetrate through the conductive enhancement layer and is in contactwith the field passivation layer.

In some embodiments, a groove is provided within the first fieldpassivation sub-layer, and the conductive enhancement layer isconfigured to fill the groove. In this way, it is beneficial to ensurethat the solar cell has a relatively thin thickness while having therelatively high conversion efficiency.

In some embodiments, the conductive enhancement layer includes a firstconductive enhancement sub-layer and a second conductive enhancementsub-layer disposed in sequence, the first conductive enhancementsub-layer is configured to cover a surface of the groove, a contactresistance between the first conductive enhancement sub-layer and thefield passivation layer is smaller than a contact resistance between thesecond enhancement sub-layer and the field passivation layer, and aresistivity of the second enhancement sub-layer is smaller than aresistivity of the first enhancement sub-layer.

In some embodiments, the field passivation layer is configured to exposepart of a surface of the first interface passivation sub-layer, theconductive enhancement layer is in contact with the exposed part of thesurface of the first interface passivation sub-layer, and theresistivity of the material of the conductive enhancement layer issmaller than a resistivity of a material of the interface passivationlayer.

In some embodiments, the first interface passivation sub-layer includesa plurality of discontinuous local surfaces exposed by the fieldpassivation layer, and the conductive enhancement layer is in contactwith the plurality of discontinuous local surfaces.

In some embodiments, the conductive enhancement layer has a fieldpassivation capability. In this way, a field passivation capability ofthe field passivation layer may be compensated to a certain extent, soas to ensure that the solar cell has a relatively high field passivationeffect as a whole, thereby further ensuring that the solar cell has therelatively high conversion efficiency.

In some embodiments, the resistivity of the material of the conductiveenhancement layer is further smaller than a resistivity of a material ofthe interface passivation layer.

In some embodiments, a material type of the conductive enhancement layerincludes at least one of: a conductive polymer, a metal silicide or anoxidized conductor.

In some embodiments, the conductive enhancement layer is a multilayerstructure comprising a plurality of film layers, wherein the pluralityof film layers are disposed in a direction perpendicular to the surfaceof the substrate.

In some embodiments, the conductive enhancement layer includes a firstconductive enhancement sub-layer and a second conductive enhancementsub-layer disposed in sequence in a direction away from the substrate;wherein a contact resistance between the first conductive enhancementsub-layer and the interface passivation layer is smaller than a contactresistance between the second conductive enhancement sub-layer and theinterface passivation layer; a resistivity of the second conductiveenhancement sub-layer is smaller than a resistivity of the firstconductive enhancement sub-layer.

In some embodiments, the conductive enhancement layer further includes athird conductive enhancement sub-layer that is disposed between thesecond conductive enhancement sub-layer and the field passivation layer;wherein a contact resistance between the third conductive enhancementsub-layer and the field passivation layer is smaller than a contactresistance between the second conductive enhancement sub-layer and thefield passivation layer; the resistivity of the second conductiveenhancement sub-layer is smaller than a resistivity of the thirdconductive enhancement sub-layer.

In some embodiments, the conductive enhancement layer is in contact withthe second electrode.

In some embodiments, the conductive enhancement layer is separated fromthe second electrode by an air gap.

In some embodiments, the groove is arc-shaped, and an opening width ofthe groove is at least equal to a width of the first field passivationsub-layer and a width of the first interface passivation sub-layer in anarrangement direction of adjacent second electrodes.

In some embodiments, the groove has a square shape, and the openingwidth of the groove is smaller than a thickness of the first fieldpassivation sub-layer.

Compared with the existing technology, the technical solution providedby the embodiments of the present disclosure has the followingadvantages:

In the above technical solutions, since the resistivity of the materialof the conductive enhancement layer is smaller than the resistivity ofthe material of the field passivation layer, the conductive enhancementlayer serves as a path for the carriers in the first interfacepassivation sub-layer to flow to the electrode, which is conducive toenabling the carriers to flow to the electrode at the relatively fasttransmission rate and the relatively low transmission loss, therebyimproving the conversion efficiency of the solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are described as examples with reference to thecorresponding figures in the accompanying drawings, and the examples donot constitute a limitation to the embodiments. Elements with the samereference numerals in the accompanying drawings represent similarelements. The figures in the accompanying drawings do not constitute aproportion limitation unless otherwise stated.

FIG. 1 is a schematic structural diagram of a solar cell;

FIG. 2 is a schematic structural diagram of a solar cell according tothe present disclosure;

FIG. 3 is an enlarged view of part A in FIG. 2;

FIG. 4 is a schematic structural diagram of a solar cell according tothe present disclosure;

FIG. 5 is a schematic structural diagram of a solar cell according tothe present disclosure;

FIG. 6 is a schematic structural diagram of a solar cell according tothe present disclosure;

FIG. 7 is a schematic structural diagram of a solar cell according tothe present disclosure;

FIG. 8 is a schematic structural diagram of a solar cell according tothe present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, FIG. 1 is a schematic structural diagram of a solarcell.

As shown in FIG. 1, the solar cell includes a substrate 10, and aninterface passivation layer 121, a field passivation layer 122 andelectrode(s) 123 that are sequentially disposed on a rear surface of thesubstrate 10. The interface passivation layer 121 includes a firstinterface passivation sub-layer 121 a corresponding to the interfacepassivation layer between adjacent electrodes 123 and a second interfacepassivation sub-layer 121 b corresponding to the interface passivationlayer between the electrode 123 and the substrate 10. The fieldpassivation layer 122 includes a first field passivation sub-layer 122 acorresponding to the field passivation layer between adjacent electrodes123 and a second field passivation sub-layer 122 b corresponding to thefield passivation layer between the electrode 123 and the substrate 10.

A transmission path of carriers to the electrode 123 is as follows: thecarriers transmitted from the substrate 10 to the first interfacepassivation sub-layer 121 a need to be vertically transmitted to thefirst field passivation sub-layer 122 a, then laterally transmittedthrough the first field passivation sub-layer 122 a, and finally reach asurface of the electrode 123 through the second field passivationsub-layer 122 b. Alternatively, the carriers need to be laterallytransmitted within the first interface passivation sub-layer 121 a, andthen vertically pass through the second field passivation sub-layer 122b after reaching the second interface passivation sub-layer 121 b toreach the surface of electrode 123. Since the interface passivationlayer 121 and the field passivation layer 122 have a relatively highresistivity and a poor conductivity, a series resistance of the solarcell is relatively large, and a lateral transmission resistance formajority carriers is relatively large, problems such as a relativelyslow transmission rate, a long transmission time, and a relatively largetransmission loss will occur in the lateral transmission process of themajority carriers, thus leading to a relatively low conversionefficiency of the solar cell.

In order to avoid the above technical problems, generally, a distancebetween adjacent electrodes 123 may be set smaller, however, which mayincrease a surface recombination area between the electrode 123 and thefield passivation layer 122, thus causing negative impact on the fieldpassivation effect of the field passivation layer 122 and the conversionefficiency of the solar cell. In addition, the smaller the distancebetween the adjacent electrodes 123 may cause that more electrodes 123need be provided on the field passivation layer 122 with the same width,that is, more metal electrode materials need to be consumed in thefabrication of the solar cell, and a fabrication cost of the solar cellis increased.

It should be noted that the two transmission paths mentioned above areonly a specific example of the transmission path of the carriers, andthe actual transmission path of the carriers may also be an obliquetransmission. In this case, the actual transmission path of the carriersmay be equivalent to the lateral transmission and the verticaltransmission, that is, the carriers may be considered to be laterallytransmitted in the first interface passivation sub-layer 121 a or thefirst field passivation sub-layer 122 a.

Embodiments of the present disclosure provide a solar cell, in which aconductive enhancement layer with a relatively low resistivity isarranged on a side of the first interface passivation sub-layer awayfrom the substrate, so as to serve as a path for the carriers in thefirst interface passivation sub-layer to flow to the electrode, which isconducive to enabling the carriers to flow to the electrode at arelatively fast rate and with a relatively small loss, thereby improvinga conversion efficiency of the solar cell.

The embodiments of the present disclosure will be described in detailbelow with reference to the accompanying drawings in order to make theobjectives, technical solutions and advantages of the present disclosureclearer. However, those skilled in the art may appreciate that, in thevarious embodiments of the present disclosure, numerous technicaldetails are set forth in order to provide the reader with a betterunderstanding of the present disclosure. However, the technicalsolutions claimed in the present disclosure may be implemented withoutthese technical details and various changes and modifications based onthe following embodiments.

FIG. 2 is a schematic structural diagram of a solar cell provided in thepresent disclosure.

Referring to FIG. 2, the solar cell includes a substrate 20, aninterface passivation layer 221 covering a rear surface of the substrate20, a second electrode 225 disposed at a side of the interfacepassivation layer 221 facing away from the substrate 20, a fieldpassivation layer 223, and a conductive enhancement layer 222. Theinterface passivation layer 221 includes a first interface passivationsub-layer 221 a and a second interface passivation sub-layer 221 b. Thefirst interface passivation sub-layer 221 a corresponds to a portion ofthe interface passivation layer between adjacent second electrodes 225and the second interface passivation sub-layer 221 b corresponds to aportion of the interface passivation layer between the substrate 20 andthe second electrode 225. The field passivation layer 223 is at leastpartially disposed between the interface passivation layer 221 and thesecond electrode 225. The conductive enhancement layer 222 is at leastpartially disposed at a side of the first interface passivationsub-layer 221 a away from the substrate 20, for carriers in the firstinterface passivation sub-layer 221 a to flow to the second electrode225. A resistivity of a material of the conductive enhancement layer 222is smaller than a resistivity of a material of the field passivationlayer 223, and the resistivity of the material of the conductiveenhancement layer 222 is smaller than 0.001 Ω·cm.

The solar cell further includes an emitter 211, a first passivation film212, an antireflection film 213, and a first electrode 214 sequentiallydisposed on a front surface of the substrate 20, and a secondpassivation film 224 disposed at a side of the field passivation layer223 away from the substrate 20.

As used herein, a front surface refers to a light-receiving surface thatfaces to the sun during a normal operation, and a real surface of thesubstrate is opposite to the front surface.

The substrate 20 and the emitter 211 form a PN junction. Specifically,if the substrate 20 is P-type, the emitter 211 may be N-type; and if thesubstrate 20 is N-type, the emitter may be P-type. Optionally, amaterial of the substrate 20 may include a semiconductor material suchas a monocrystalline silicon, a polycrystalline silicon, amonocrystalline-like silicon, a perovskite, etc.

A type of a doped ion of the field passivation layer 223 is the same asa type of a doped ion of the substrate 20. Specifically, when thesubstrate 20 is an N-type silicon wafer, the field passivation layer 223is an N-type doped layer (such as an N-type doped polysilicon), and thedoped ion includes group V elements such as a phosphorus ion. When thesubstrate 20 is a P-type silicon wafer, the field passivation layer 223is P-type doped (such as a P-type doped polysilicon), and the doped ionincludes group III elements such as a boron ion.

The materials of the first passivation film 212 and the secondpassivation film 224 include one or more materials such as a siliconnitride, a silicon oxynitride, a silicon carbonitride, a titanium oxide,a hafnium oxide, an aluminum oxide, etc. A material of theantireflection film 213 may include one or more materials such as thesilicon nitride, the silicon oxynitride, the silicon carbonitride, etc.The first electrode 214 penetrates through the antireflection film 213and the first passivation film 212 and is connected with the emitter211. The second electrode 225 penetrates through the second passivationfilm 224 and is in contact with the field passivation layer 223. Thefirst electrode 214 may be a silver-aluminum electrode, and the secondelectrode 225 may be a silver electrode.

In this embodiment, in a direction away from the rear surface of thesubstrate 20, the interface passivation layer 221, the conductiveenhancement layer 222, the field passivation layer 223 and the secondpassivation film 224 are sequentially disposed. The second electrode 225penetrates through the second passivation film 224 and is in contactwith the field passivation layer 223.

Since the second electrode 225 is attractive to majority carriers in theinterface passivation layer 221, the majority carriers in the interfacepassivation layer 221 may orderly pass through the conductiveenhancement layer 222 and the field passivation layer 223, that is, flowto the second electrode 225 in a form of an orderly current.Accordingly, since the current flows in an orderly manner between theinterface passivation layer 221, the conductive enhancement layer 222and the field passivation layer 223, it may be considered that theconductive enhancement layer 222 is in an electrical contact with theinterface passivation layer 221, and the conductive enhancement layer222 is used for the carriers in the first interface passivationsub-layer 221 a to flow to the second electrode 225.

According to the above description, the conductive enhancement layer 222serves as a path for the carriers in the first interface passivationsub-layer 221 a to flow to the second electrode 225. Specifically, inthe process of flowing to the second electrode 225, majority carriers inthe first interface passivation sub-layer 221 a may be verticallytransmitted into the conductive enhancement layer 222 first, thenlaterally transmitted through the conductive enhancement layer 222.Subsequently, the majority carriers only need to vertically pass throughthe field passivation layer 223 to reach the second electrode 225, thuscompleting a photoelectric conversion.

That is to say, in the process of flowing to the second electrode 225,the majority carriers in the first interface passivation sub-layer 221 ano longer need be transmitted laterally in the field passivation layer223, but may be transmitted laterally through the conductive enhancementlayer 222 with a lower resistivity. In this way, it is beneficial toreduce a lateral transmission resistance of the majority carriers,thereby improving a transmission rate of the majority carriers andreducing a transmission loss of the majority carriers, and furtherimproving a conversion efficiency of the solar cell.

In this embodiment, the interface passivation layer 221 may be adielectric layer with a tunneling effect, for example, a tunneling oxidelayer (such as the silicon oxide, the aluminum oxide, the hafnium oxide,etc.), a tunneling nitride layer (such as the silicon nitride), etc. Insome embodiments, a thickness of the interface passivation layer 221 isrelatively thin in order to achieve the tunneling effect, for example,the thickness is 1-4 nm. In this embodiment, a resistance of thematerial of the conductive enhancement layer 222 is smaller than 0.001Ω·cm, for example, 0.0005 Ω·cm, 0.0002 Ω·cm or 0.00001 Ω·cm.

In this embodiment, the resistivity of the material of the conductiveenhancement layer 222 is also smaller than a resistivity of a materialof the interface passivation layer 221. Since the carriers always tendto be transmitted along a path with the lowest resistance during thetransmission process, when the resistivity of the conductive enhancementlayer 222 is smaller than that of the interface passivation layer 221,the majority carriers in the first interface passivation sub-layer 221 amay be preferentially transmitted laterally through the conductiveenhancement layer 222, which is conducive to further improving anaverage transmission rate of the majority carriers, reducing an averagetransmission resistance of the majority carriers and improving theconversion efficiency of the solar cell.

In this embodiment, the material type of the conductive enhancementlayer 222 includes a conductive polymer, a metal silicide or an oxidizedconductor. Specifically, the conductive polymer includes a polyaniline,a polypyrrole, a polythiophene, etc., the metal silicide includes atitanium tungsten silicide, a titanium silicide, a cobalt silicide, anickel silicide, etc., and the oxidized conductor includes a indium tinoxide (ITO), an aluminum-doped zinc oxide (AZO), a CdOx, an InOx, aSnOx, a ZnO, etc.

In this embodiment, as shown in FIG. 3, the conductive enhancement layer222 has a multilayer structure. A plurality of film layers in themultilayer structure are disposed in a direction perpendicular to thesurface of the substrate 20, and materials of different film layers arethe same or different. Herein, a single film layer may be composed of asingle material or multiple materials, so as to better meet a presetperformance requirement.

Specifically, the conductive enhancement layer 222 may include a firstconductive enhancement sub-layer 2221 and a second conductiveenhancement sub-layer 2222 disposed in sequence in a direction away fromthe substrate 20. A contact resistance between the first conductiveenhancement sub-layer and the interface passivation layer 221 is smallerthan a contact resistance between the second conductive enhancementsub-layer and the interface passivation layer 221. A resistivity of thesecond conductive enhancement sub-layer is smaller than a resistivity ofthe first conductive enhancement sub-layer. In this way, it isbeneficial to reduce a loss of the majority carriers when passingthrough an interface between the interface passivation layer 221 and theconductive enhancement layer 222, thereby increasing the number of themajority carriers that may reach a surface of the second electrode 225and improving the conversion efficiency of the solar cell.

Further, the conductive enhancement layer 222 may further include athird conductive enhancement sub-layer 2223 which is disposed betweenthe second conductive enhancement sub-layer and the field passivationlayer 223. A contact resistance between the third conductive enhancementsub-layer and the field passivation layer 223 is smaller than a contactresistance between the second conductive enhancement sub-layer and thefield passivation layer 223. The resistivity of the second conductiveenhancement sub-layer is smaller than a resistivity of the thirdconductive enhancement sub-layer. In this way, it is beneficial toreduce the loss of the majority carriers when passing through aninterface between the conductive enhancement layer 222 and the fieldpassivation layer 223, thereby further increasing the number of themajority carriers that may reach the surface of the second electrode 225and improving the conversion efficiency of the solar cell.

The conductive enhancement layer 222 may be formed by a high-temperaturethermal diffusion process, an ion implantation process, a physical vapordeposition (PVD) process, a chemical vapor deposition (CVD) process, anatomic layer deposition (ALD) process, a sol-gel method and othermethods.

In some embodiments, a field passivation layer may cover a surface of asecond interface passivation sub-layer facing away from the substrate.The following will be described in detail below with reference to FIG.4. Parts that are the same as or corresponding to the previousembodiment may refer to the corresponding description of the previousembodiment, and will not be repeated below.

In this embodiment, a conductive enhancement layer 322 covers a surfaceof a first interface passivation sub-layer 321 a facing away from asubstrate 30. A second field passivation sub-layer 323 b covers part ofa surface of a second interface passivation sub-layer 321 b facing awayfrom the substrate 30. A second electrode 325 is in contact with asurface of the second field passivation sub-layer 323 b facing away fromthe substrate 30. At least part of the conductive enhancement layers 322is disposed between adjacent second electrodes 325. The conductiveenhancement layer 322 is in contact with a side wall of the secondelectrode 325. Herein, the second field passivation sub-layer 323 b iscloser to the substrate 30 than the first field passivation sub-layer323 a, which is beneficial to enhance an overall field passivationeffect of the field passivation layer 323. Besides, the conductiveenhancement layer 322 is in contact with the second electrode 325, andmajority carriers may directly reach a surface of the second electrode325 through the conductive enhancement layer 322 without passing throughthe field passivation layer 323, which is beneficial to further reduce atransmission resistance of the majority carriers and reduce atransmission loss of the majority carriers.

In this embodiment, in a direction perpendicular to a rear surface ofthe substrate 30, a thickness of the first field passivation sub-layer323 a is the same as a thickness of the second field passivationsub-layer 323 b, and a thickness of the conductive enhancement layer 322is greater than a thickness of the second field passivation sub-layer323 b. In other embodiments, the thickness of the second fieldpassivation sub-layer is smaller than the thickness of the first fieldpassivation sub-layer, and a contact area between the second electrodeand the conductive enhancement layer is controlled by controlling thethickness of the second field passivation sub-layer.

In this embodiment, the first field passivation sub-layer 323 a isseparated from the second field passivation sub-layer 323 b. In otherembodiments, the first field passivation sub-layer is connected with thesecond field passivation sub-layer. Specifically, a width of an openingin the conductive enhancement layer is widened and a deposition processis adopted to simultaneously form the first field passivation sub-layerand the second field passivation sub-layer. At this time, the firstfield passivation sub-layer also covers a side wall of the conductiveenhancement layer. The first field passivation sub-layer separates theconductive enhancement layer from the second electrode, and a width ofthe second electrode remains unchanged. Alternatively, the depositionprocess is directly performed to simultaneously form the first fieldpassivation sub-layer and the second field passivation sub-layer. Atthis time, the second field passivation sub-layer also covers the sidewall of the conductive enhancement layer. The second field passivationsub-layer separates the conductive enhancement layer from the secondelectrode, and the width of the second electrode is narrowed.

In this embodiment, in a horizontal interface parallel to the rearsurface of the substrate 30, the conductive enhancement layer 322 hasthe same material at different positions. In other embodiments, in thehorizontal interface parallel to the rear surface of the substrate, theconductive enhancement layer has different materials at differentpositions. Specifically, by adjusting a material of a surface layerwhere the conductive enhancement layer is in contact with the secondelectrode, the conductive enhancement layer has a relatively smallseries resistance in a lateral direction, and a contact resistancebetween the conductive enhancement layer and the second electrode isrelatively small, thereby reducing the loss of the majority carrierspassing through the interface and improving the conversion efficiency ofthe solar cell.

In other embodiments, the thickness of the second field passivationsub-layer may also be greater than the thickness of the conductiveenhancement layer, that is, the second electrode does not contact withthe conductive enhancement layer.

In some embodiments, a field passivation layer may cover a surface of aninterface passivation layer facing away from the substrate. Thefollowing will be described in detail below with reference to FIG. 5.Parts that are the same as or corresponding to the previous embodimentmay refer to the corresponding description of the previous embodiment,and will not be repeated below.

In this embodiment, an interface passivation layer 421, a fieldpassivation layer 423, and a conductive enhancement layer 422 aresequentially disposed in a direction perpendicular to a rear surface ofa substrate 40. A second electrode 425 is in contact with a surface ofthe conductive enhancement layer 422 facing away from the substrate 40.Since the conductive enhancement layer 422 is disposed at a side of thefield passivation layer 423 facing away from the substrate 40, anarrangement of the conductive enhancement layer 422 may not increase adistance between the field passivation layer 423 and the substrate 40,thus making the field passivation layer 423 have a good fieldpassivation effect.

In other embodiments, referring to FIG. 6, a second electrode 525 maypenetrate through a conductive enhancement layer 522 and contacts afield passivation layer 523, which is beneficial to shorten atransmission path of majority carriers and reduce a transmissionresistance of the majority carriers, thereby improving a conversionefficiency of the solar cell.

Herein, shortening the transmission path of the majority carriers andreducing the transmission resistance of the majority carriers include:when the second electrode 525 is only in contact with the conductiveenhancement layer 522, the majority carriers need to pass through aninterface between the field passivation layer 523 and the conductiveenhancement layer 522 and an interface between the conductiveenhancement layer 522 and the second electrode 525 so as to enter thesecond electrode 525. When the second electrode 525 is in contact withthe field passivation layer 523, the majority carriers only need to passthrough the interface between the field passivation layer 523 and thesecond electrode 525 to enter the second electrode 525.

In this embodiment, the conductive enhancement layer 522 is in contactwith the second electrode 525. In other embodiments, in order to reducea surface recombination loss of the solar cell, an air gap may be usedto separate the conductive enhancement layer from the second electrode.Specifically, after forming the second electrode penetrating theconductive enhancement layer, the conductive enhancement layer incontact with the second electrode may be further etched to form the airgap.

In some embodiments, a groove may be provided within a first fieldpassivation sub-layer, and a conductive enhancement layer fills thegroove. The following will be described in detail below with referenceto FIG. 7. Parts that are the same as or corresponding to the previousembodiment may refer to the corresponding description of the previousembodiment, and will not be repeated below.

In this embodiment, a groove 623 c is provided within a first fieldpassivation sub-layer 623 a, and a conductive enhancement layer 622fills the groove 623 c. In this way, a transmission path of majoritycarriers vertically transmitted from a first interface passivationsub-layer 621 a to the conductive enhancement layer 622 may beshortened, thereby reducing a transmission resistance of the majoritycarriers, shortening a transmission time, reducing a transmission lossand improving a conversion rate of the solar cell. Besides, since anarrangement of the conductive enhancement layer 622 does not increase athickness of the solar cell in a direction perpendicular to a surface ofa substrate 60, it may ensure that the solar cell has a relatively thinthickness and a relatively small size.

In this embodiment, the groove 623 c is an arc-shaped groove with anarc-shaped side wall and a bottom surface, and an opening width of thegroove 623 c is equal to a width of the first field passivationsub-layer 623 a and a width of the first interface passivation sub-layer621 a in an arrangement direction of adjacent second electrodes 625. Inother embodiments, the groove is a square groove with a vertical sidewall and a horizontal bottom surface. Alternately, the opening width ofthe groove may be smaller than a thickness of the first fieldpassivation sub-layer. Alternately, the conductive enhancement layer maynot fully fill the groove.

Herein, the arc-shaped groove may be formed by a wet etching process,and the square groove may be formed by a dry etching process.

It should be noted that the field passivation layer 623 may also havethe groove 623 c with the opening width larger than the width of thefirst field passivation sub-layer 623 a. In this way, the conductiveenhancement layer 622 is in contact with the second electrode 625, andthe majority carriers do not need to pass through a second fieldpassivation sub-layer 623 b with a relatively high resistivity, which isconducive to reducing the transmission resistance of the majoritycarriers, reducing the transmission loss of the majority carriers andimproving the conversion efficiency of the solar cell.

In this embodiment, the conductive enhancement layer 622 includes afirst conductive enhancement sub-layer (not shown) and a secondconductive enhancement sub-layer (not shown) which are sequentiallydisposed in a direction away from the substrate 60. The first conductiveenhancement sub-layer covers a surface of the groove 623 c. A contactresistance between the first conductive enhancement sub-layer and thefield passivation layer is smaller than a contact resistance between thesecond conductive enhancement sub-layer and the field passivation layer.A resistivity of a material of the second conductive enhancementsub-layer is less than a resistivity of a material of the firstconductive enhancement sub-layer.

In this embodiment, a doped ion concentration of a surface layer of aside wall and bottom of the groove 623 c is smaller than a doped ionconcentration of a surface layer of the second field passivationsub-layer 623 b facing away from the substrate 60, thereby weakening alight absorption ability of the second field passivation sub-layer 623 band improving the conversion efficiency of the solar cell. In otherembodiments, the doped ion concentration of the surface layer of theside wall and the bottom of the groove is equal to the doped ionconcentration of the surface layer of the second field passivationsub-layer facing away from the substrate. Since a surface of the grooveis relatively close to a rear surface of the substrate, the doped ionconcentration of the surface layer of the groove and the rear surface ofthe second field passivation sub-layer are set to be same, which isconductive to compensating for the problem of a weakening of a fieldpassivation effect caused by a partial loss of the first fieldpassivation sub-layer, and ensuring that the first field passivationsub-layer has a good field passivation effect.

Specifically, in this embodiment, after a polysilicon layer is formed ona surface of the interface passivation layer, the doped ion is implantedinto a surface layer of the polysilicon layer facing away from thesubstrate 60, and the doped ion may gradually diffuse toward thesubstrate 60 due to an existence of a concentration difference, therebyforming the field passivation layer 623. After forming the fieldpassivation layer 623, the wet etching process is performed on the firstfield passivation sub-layer 623 a to form the arc-shaped groove 623 c,and the etching is continued until the surface of the first interfacepassivation sub-layer 621 a is exposed. In other embodiments, after thepolysilicon layer is formed, part of the polysilicon layer may be etchedto form a groove, and then the ion is implanted into a surface layer ofthe polysilicon layer with the groove away from the substrate to formthe field passivation layer.

In this embodiment, the first field passivation sub-layer 623 a exposespart of the surface of the first interface passivation sub-layer 621 a.The conductive enhancement layer 622 filled in the groove 623 is incontact with the exposed part of the surface of the first interfacepassivation sub-layer 621 a. A resistivity of a material of theconductive enhancement layer 622 is smaller than a resistivity of amaterial of the first interface passivation sub-layer 621 a. In thisway, the majority carriers may be directly transmitted from the firstinterface passivation sub-layer 621 a to the conductive enhancementlayer 622 without passing through the field passivation layer 623 with arelatively large resistivity, which is conductive to reducing thetransmission resistance of the majority carriers, reducing thetransmission loss of the majority carriers and improving the conversionefficiency of the solar cell.

In this embodiment, the material of the first interface passivationsub-layer 621 a is the same as a material of the second interfacepassivation sub-layer 621 b, and both are formed by the same formingprocess. In other embodiments, the material of the first interfacepassivation sub-layer 621 a may be different from the material of thesecond interface passivation sub-layer 621 b.

In addition, when the material of the field passivation layer 623 is adoped polysilicon, an amorphous silicon or a monocrystalline silicon, ametal silicide may be formed by directly doping a metal material toserve as the conductive enhancement layer.

In this embodiment, the exposed part of the surface of the firstinterface passivation sub-layer 621 a is a continuous surface. In otherembodiments, referring to FIG. 8, a first interface passivationsub-layer 721 a may have a plurality of discontinuous local surfacesexposed by a first field passivation sub-layer 723 a. A conductiveenhancement layer 722 is in contact with the plurality of discontinuouslocal surfaces, so that carriers in the first interface passivationsub-layer 721 a may be transmitted to the conductive enhancement layer722 through a relatively short path.

In this embodiment, the conductive enhancement layer 622 has a fieldpassivation capability, which is conductive to ensuring that anyposition on the rear surface of the substrate 60 is subjected to a fieldpassivation, thereby ensuring a selective transmission of the carriers.Herein, the field passivation capability of the conductive enhancementlayer 622 may be obtained by forming a positive charge and using amaterial with a band difference compared with the material of thesubstrate 60.

In this embodiment, since the resistivity of the material of theconductive enhancement layer is smaller than the resistivity of thematerial of the field passivation layer, the conductive enhancementlayer serves as a path for the carriers in the first interfacepassivation sub-layer to flow to the electrode, which is conductive toenabling the carriers to flow to the electrode at a relatively fast ratewith a relatively small loss, thereby improving the conversionefficiency of the solar cell.

Those skilled in the art should appreciate that the aforementionedembodiments are specific embodiments for implementing the presentdisclosure. In practice, however, various changes may be made in theforms and details of the specific embodiments without departing from thespirit and scope of the present disclosure. Any person skilled in theart may make their own changes and modifications without departing fromthe spirit and scope of the present disclosure, so the protection scopeof the present disclosure shall be subject to the scope defined by theclaims.

What is claimed is:
 1. A solar cell, comprising: a substrate; aninterface passivation layer on a rear surface of the substrate, whereinthe interface passivation layer includes a first interface passivationsub-layer and a second interface passivation sub-layer; at least oneelectrode disposed at a side of the interface passivation layer facingaway from the substrate, the first interface passivation sub-layercorresponding to a portion of the interface passivation layer betweenadjacent electrodes, and the second interface passivation sub-layercorresponding to a portion of the interface passivation layer betweenthe substrate and the at least one electrode; a field passivation layer,at least partially disposed between the interface passivation layer andthe at least one electrode; and a conductivity enhancement layer, atleast partially disposed at a side of the first interface passivationsub-layer facing away from the substrate, and configured to enablecarriers in the first interface passivation sub-layer to flow to the atleast one electrode, wherein a resistivity of a material of theconductivity enhancement layer is smaller than a resistivity of amaterial of the field passivation layer, and the resistivity of thematerial of the conductivity enhancement layer is smaller than 0.001Ω·cm.
 2. The solar cell according to claim 1, wherein the conductivityenhancement layer is configured to cover a surface of the interfacepassivation layer facing away from the substrate; the field passivationlayer is configured to cover a surface of the conductivity enhancementlayer facing away from the substrate; and the at least one electrode isconfigured to contact with the field passivation layer.
 3. The solarcell according to claim 1, wherein the interface passivation layer is adielectric layer with a tunneling effect, and the interface passivationlayer is selected from a tunneling oxide layer or a tunneling nitridelayer; and the interface passivation layer has a thickness of 1 to 4 nm.4. The solar cell according to claim 1, wherein the material of theconductivity enhancement layer includes at least one of: a conductivepolymer, a metal silicide and an oxidized conductor.
 5. The solar cellaccording to claim 4, wherein the conductive polymer includes at leastone of polyaniline, polypyrrole, polythiophene; the metal silicideincludes at least one of titanium tungsten silicide, titanium silicide,cobalt silicide, nickel silicide; and the oxidized conductor includes atleast one of ITO, AZO, CdOx, InOx, SnOx, ZnO.
 6. The solar cellaccording to claim 1, wherein the resistivity of the material of theconductivity enhancement layer is further smaller than a resistivity ofa material of the interface passivation layer.
 7. The solar cellaccording to claim 2, wherein the conductivity enhancement layer is amultilayer structure including a plurality of film layers, wherein theplurality of film layers are disposed in a direction perpendicular tothe rear surface of the substrate.
 8. The solar cell according to claim7, wherein the conductivity enhancement layer includes a firstconductivity enhancement sub-layer and a second conductivity enhancementsub-layer disposed in sequence in a direction away from the substrate;wherein a contact resistance between the first conductivity enhancementsub-layer and the interface passivation layer is smaller than a contactresistance between the second conductivity enhancement sub-layer and theinterface passivation layer; a resistivity of the second conductivityenhancement sub-layer is smaller than a resistivity of the firstconductivity enhancement sub-layer.
 9. The solar cell according to claim7, wherein the conductivity enhancement layer further includes a thirdconductivity enhancement sub-layer that is disposed between the secondconductivity enhancement sub-layer and the field passivation layer;wherein a contact resistance between the third conductivity enhancementsub-layer and the field passivation layer is smaller than a contactresistance between the second conductivity enhancement sub-layer and thefield passivation layer; the resistivity of the second conductivityenhancement sub-layer is smaller than a resistivity of the thirdconductivity enhancement sub-layer.
 10. The solar cell according toclaim 1, wherein the field passivation layer is configured to cover asurface of the interface passivation layer facing away from thesubstrate, wherein the field passivation layer includes a first fieldpassivation sub-layer corresponding to a portion of the fieldpassivation layer between adjacent electrodes and a second fieldpassivation sub-layer corresponding to a portion of the fieldpassivation layer between the substrate and the at least one electrode;and the conductivity enhancement layer is configured to cover at leastpart of the surface of the first field passivation sub-layer facing awayfrom the substrate.
 11. The solar cell according to claim 10, whereinthe conductivity enhancement layer is in contact with the at least oneelectrode.
 12. The solar cell according to claim 10, wherein theconductivity enhancement layer is separated from the at least oneelectrode by an air gap.
 13. The solar cell according to claim 10,wherein the conductivity enhancement layer is configured to cover thesurface of the field passivation layer facing away from the substrate.14. The solar cell according to claim 10, wherein a groove is providedwithin the first field passivation sub-layer and the conductivityenhancement layer is configured to fill the groove.
 15. The solar cellaccording to claim 14, wherein the conductivity enhancement layer is incontact with the at least one electrode.
 16. The solar cell according toclaim 14, wherein a doped ion concentration of a surface layer of a sidewall and bottom of the groove is smaller than or equal to a doped ionconcentration of a surface layer of the second field passivationsub-layer facing away from the substrate.
 17. The solar cell accordingto claim 14, wherein a material of the field passivation layer is atleast one of doped polysilicon, amorphous silicon and monocrystallinesilicon, and a material of the conductivity enhancement layer is metalsilicide formed by directly doping a metal material to the fieldpassivation layer.
 18. The solar cell according to claim 14, wherein thegroove is arc-shaped, and an opening width of the groove is at leastequal to a width of the first field passivation sub-layer and a width ofthe first interface passivation sub-layer in an arrangement direction ofadjacent second electrodes.
 19. The solar cell according to claim 14,wherein the groove has a square shape, and the opening width of thegroove is smaller than a thickness of the first field passivationsub-layer.
 20. The solar cell according to claim 1, wherein the solarcell further comprises an emitter, a first passivation film, anantireflection film, and at least one electrode sequentially disposed ona front surface of the substrate, and a second passivation film disposedat a side of the field passivation layer facing away from the substrate.